1. Field of the Invention
Aspects of the present invention relate to a driving device for rear wheels of a 4 wheel driving electric vehicle. More particularly, aspects of the present invention relate to a driving device for rear wheels of a 4 wheel driving electric vehicle, which can minimize a loss in the drive power during 4-wheel driving by transmitting the drive power to the rear wheels based on a disconnector input shaft, rather than a clutch, after synchronizing a rotating speed of the disconnector input shaft based on a first motor with a rotating speed of a hub based on rear wheels, and can prevent a loss in the drive power during 2-wheel driving by preventing a load based on a differential device from being generated by connecting the differential device between a reduction gear group and the disconnector input shaft.
2. Description of the Related Art
In general, a 4-wheel drive vehicle may be divided into a 2-wheel drive mode and a 4-wheel drive mode according to the drive mode.
A 2-wheel drive vehicle will first be described. The 2-wheel drive vehicle is classified as a rear engine rear drive (RR) system, a front engine front drive (FF) system, or a front engine rear drive (FR) system according to actual driven wheels in the engine and transmission layouts.
Since the RR system is usually applied to only sports cars, rather than general passenger cars or sport utility vehicles (SUVs), the 2-wheel drive vehicle may be largely divided into the FF system and the FR system mode.
The FF vehicle and the FR vehicle are the same with each other in that their engines and transmissions are installed on the front sides of the vehicles, while having different layouts. That is to say, the FF vehicle is usually configured such that its engine and transmission are installed on a lateral side of the vehicle to transfer power to front wheels through a differential unit integrally formed with the transmission. The FR vehicle is generally configured such that its engine and transmission are arranged in a front-back direction of the vehicle to transfer power from the transmission to rear wheels through a propeller shaft.
Next, a 4-wheel drive vehicle will now be described. In order to supply 4 wheels with an appropriate amount of drive power of an engine, the 4-wheel drive vehicle employs a clutch, a transmission device and a differential device. The 4-wheel drive vehicle is divided into a part time 4-wheel drive vehicle and a full time 4-wheel drive vehicle according to the transmission method of the transmission. In the part time 4-wheel drive vehicle, power transferred to front wheels is manually switched. In the full time 4-wheel drive vehicle, 4 wheels are constantly driven.
In the 4-wheel drive vehicle, the power transferred from the engine is distributed to front and rear wheels. As shown in FIG. 1, electric vehicles, including a hybrid vehicle, generally use the drive power generated from a separate motor (M) driven by a battery (B), rather than the drive power generated from an engine (E) and transferred to rear wheels. The drive power generated from the engine (E) is transferred to a transmission (TM) to then be applied to front wheels through a differential device (D).
FIG. 2 is a perspective view of a conventional driving device for rear wheels of the conventional 4 wheel driving electric vehicle shown in FIG. 1.
As shown in FIG. 2, the conventional driving device includes a motor 1 generating rotational power to drive a vehicle, a first drive gear 2 connected to a rotation shaft of the motor 1, a first driven gear 3 meshed with the first drive gear 2, a second drive gear 4 coaxially coupled to the first driven gear 3, a second driven gear 5 meshed with the second drive gear 4, a clutch 6 coaxially coupled to the second driven gear 5 and transferring or blocking drive power, and a differential gear 7 connected to the clutch 6 to transfer the drive power to both wheels.
With this configuration, the conventional driving device operates as follows. When the motor 1 is driven, the power generated from the motor 1 is transferred to the first drive gear 2 and is primarily decelerated by the first driven gear 3 meshed with the first drive gear 2.
The power primarily decelerated by the first driven gear 3 is transferred to the second drive gear 4 coaxially coupled to the first driven gear 3 and is secondarily decelerated by the second driven gear 5 meshed with the second drive gear 4.
The power secondarily decelerated by the second driven gear 5 is coaxially coupled to the second driven gear 5 to then be transferred to the clutch 6 transferring or blocking drive power. The front wheels of the vehicle are driven by the power generated from a front wheel drive motor (not shown) or an engine (not shown) and the vehicle runs. Then, if the power is transferred by the clutch 6 for 4-wheel driving, the power is transferred to both rear wheels by the differential gear 7 connected to the clutch 6, thereby achieving the 4-wheel driving.
In the conventional driving device, however, since the power is transferred using a clutch, a loss in the drive power may be generated due to a slip between friction plates in the clutch.
In addition, in the conventional driving device, since a differential gear is connected between the clutch and rear wheels, a load derived from the differential gear may be generated during 2-wheel driving using front wheels, resulting in a loss in the drive power.